Rolls are prone to various surface defects during rolling due to multiple operating conditions. Particularly for the backup roll necks of cold rolling mills, FCDP four-row cylindrical roller bearings are widely adopted for radial load-bearing owing to high rolling force and speed. The bearing inner ring is typically mounted onto the roll neck with a shrink-fit interference assembly.

Surface defects on the roll neck directly undermine the interference fit, leading to a series of failures such as bearing inner ring creep (slippage), inner ring cracking, bearing seizure, and roll neck burning. Therefore, inspection, maintenance, and restoration of roll necks are critically important.

As shown in the figures, these are the backup roll necks of a 900 six-high cold rolling mill (designed for mounting bearing inner rings). Magnified observation reveals obvious steps, fine cracks, and uneven roughness on the roll neck surface.

Rolls in this condition must NOT be put into service. The roll neck serves as the mounting datum for the bearing inner ring. Such defects are highly likely to induce creep of the bearing inner ring, which may result in inner ring cracking in mild cases, or bearing seizure and burnout, even roll breakage accidents in severe cases.

The above figure shows the work roll neck of a 900 six-high cold rolling mill, with obvious spalling on the surface. Restricted by radial dimension, this type of work roll neck lacks sufficient space for mounting a bearing inner ring. For this reason, the roll neck surface is hardened and directly used as the mounting datum for the bearing outer ring, while the bearing rolling elements run within the bearing raceways.

Severe spalling on the roll neck surface directly impairs the operating conditions of the bearing, causing failures such as cage deformation and rolling element shedding or fracture.

For roll necks with the above defects, continued use is not recommended. Two treatment solutions are provided:

1.    Customize non-standard roll necks, with matched non-standard bearing inner diameters or outer rings supplied by bearing manufacturers.

2.    Perform surface restoration on the roll neck to resume its original design dimensions and surface precision.